Mechanical time fuse



Dec. W42. N., M. LAKE 2,304,

MECHANI CAL TIME FUSE Filed April 15, 1937 3 Sheets-Sheet l FIG ATTORNEYS Dec. 8, 1942.

Fl G. 3

' N. M. LAKE 2,3U4J06 MECHANICAL TIME FUSE Filed April 15, 1937 3 Sheets-Sheet 2 &

q almm qqbbcrneys N. M. LAKE 2,304,106

MECHANICAL TIME FUSE 5 Sheets-Sheet 3 Filed A ril. 15. 19:57

aiented Dec. 8, 1942 is ares tics MECHANICAL TIME FUSE Norman M. Lake, Ashland, Pa., assignor of onetenth to Esther H. Cole, Chevy Chase, Md.

2 Claims.

This invention relates to a mechanical time fuse for explosive projectiles. It is the principal object of the invention to provide a fuse which is simple in structure, dependable in operation, and which is characterized by extreme accuracy in timing regardless of variation in the conditions under which it is used.

The fuses in common use at the present time are of the type which are dependent on the time required to burn a fuse in the form of a ring of highly compressed powder. However, it is extremely difficult if not impossible to accurately control the timing of such a fuse; among the conditions which affect the burning time of the powder may be mentioned the following:

. Uniformity in the blending of the powder;

. Seasoning of the powder both before and after loading into the time train rings;

Uniformity in loading the rings;

. Uniformity in assembly of fuse;

Velocity of projectile and rotative speed of the same;

. Temperature at time of use;

. Atmospheric pressure at time of use;

. Angle of elevation of gun.

Since the foregoing list of conditions which affect the burning time of powder in fuses of this character is not complete, it can be readily understood that there is no assurance whatever of uniform timing in such devices. Since the muzzle velocity of projectiles with which this type of fuse is used ranges between 1750 and 3000 feet per second, and since it is the opinion of ballistic engineers that only a small portion of the velocity of the projectile is lost during flight, it will be seen that if a powder ring fuse is set for a time of 15 seconds but ignites the base charge in 15 seconds, the projectile will be some 800 to 1500 feet away from the target at the instant of explosion.

A further feature of the combustion type of fuse which renders it decidedly disadvantageous is the hazard associated with the handling of the powder before and during blending, drying, loading into the rings, and assembly. It is furthermore dificult to blend the powder and to load the rings uniformly, and the seasoning of the powder is dependent on the agent. It is impossible to ac moo no.

effect accurate correction for linear velocity and z rotative speed of the projectile or to correct for temperature and atmospheric pressure.

Efforts have been made to avoid the numerous disadvantages of the combustible fuse type of timer by the employment of mechanical devices for timing the explosion. However, while such devices may have overcome some of the defects of the combustible fuse, other diiflculties, inherent in mechanical timin devices when subjected to the severe conditions imposed by use in projectiles, have arisen. For example, clockwork timing devices have been proposed, but it is obvious that a device of this character, which must be sufliciently delicate to explode a projectile within a period of time which must be controlled accurately to the fraction of a second, is not capable of withstanding the severe shocks applied to the projectile during firing and flight. Even if such devices were constructed to afford the requisite sturdiness and resistance to shock, the expense of construction would be a serious item.

It has been suggested as an alternative to employ inertia members operable by centrifugal force derived from the rotation of the projectile on its axis during flight, but one of the important difficulties encountered is the lack of uniformity of speed of rotation resulting, for example, from the firing of the projectile from different guns or guns of different type, or from the influence of wind velocity and direction on the rotational speed. Clearly a centrifugally operated timing device must be wholly independent of the rotational velocity of the projectile if it is to function satisfactorily and accurately.

It is therefore the purpose of the present invention to overcome the difficulties encountered with the timing devices heretofore proposed; with this end in view a timing device of the centrifugally operated type is employed, which device is so constructed that highly accurate timing may be secured regardless of variation in the conditions of use.

More specifically it is the object of the invention to provide a timing device which, while operable by forces derived from the speed of rotation of the projectile, will produce extremely accurate timing regardless of variation in such speed and regardless of such slight shift in the axis of rotation of the projectile as may occur during flight. In the preferred form of the invention use is made of one or more inertia members which are urged outwardly of the projectile axis under the action of centrifugal force, these inertia members being so connected to a timing or control member as to displace the latter at a predetermined rate by the application thereto of a force which is substantially constant for the various positions which the inertia member may assume. By applying constant forces of slightly different magnitude 'in opposition, displacement of the control member independent of the speed of rotation of the projectile may be established. For example, it is obvious that if we employ two inertia members of diiierent mass for the displacement of a timing or control member in such manner that the forces of the inertia members are opposed, one moving outwardly and one inwardly of the aixs of rotation of the projectile, the centrifugal force acting on these inertia members is continually varied by reason of the fact that the position of such members is constantly changing. In accordance with the present invention the centrifugal forces of the inertia members are so applied to the control member as to compensate for the shift in position of the inertia members, the magnitude of the opposing forces tending to move the control member being of constant ratio, the ratio being determined by the difference in mass of the inertia members and being independent of the speed of rotation of the projectile.

Preferably the desired result is achieved by transmitting to the control member the centrifugal force developed in the inertia members through a cam device, for example by the employment of a cam pattern based on a parabolic spiral. In the preferred form of the invention the inertia members are constituted by a plurality of spheres or balls which are constrained to move radially outward of the axis of rotation of the projectile, each such ball engaging with one of two cam surfaces formed on a rotatable control member, the cam surfaces being shaped to define parabolic spirals of opposite hand, so that the forces exerted by the balls on the control member are opposed and so that each ball exerts the same force tending to move the control member regardless of the posiiton of the ball with respect to the axis of rotation. The movement of the control member through a predetermined range of movement i utilized to fire the charge by the use of any convenient type of firing mechanism. For example, the firing mechanism may include a, firing pin which is projected toward a primer by centrifugal force, the firing pin being initially locked against displacement by means which is released after the control member has been rotated through a predetermined angle. Means are of course provided for regulating or setting the mechanism so that the range of movement of the control member may be varied with resultant variation in the timing. A device, preferably in the form of a centrifugally operated latch, is applied to the control member to prevent unintentional displacement thereof prior to the discharge of the projectile from the gun.

Further features and objects of the invention will be apparent from the following description taken in connection with the accompanying drawings, in which Figure 1 is a longitudinal section substantially on the line ll of Figure 4 of the head of a projectile containing a timing device constructed in accordance with the invention;

Figure 2 is a longitudinal sectional view taken substantially on the line 22 of Figure 4;

Figure 3 is a view partly in section on the line 3-3 of Figure Figures 4, 5, and 6 are transverse sectional views on the lines i--4, 5-5, and 6-fi respectively of Figure 1;

Figure 7 is a transverse sectional view on the line 1-7 of Figure 2;

Figure 8 is an enlarged transverse sectional view on the line 88 of Figure 1;

Figure 9 is an enlarged fragmentary view, partly in section, of certain structure shown in Figure 1;

Figure 10 is a partial transverse sectional view taken substantially on the line l0l0 of Figure l; and

Figures ll and 12 are diagrammatic views introduced for the purpose of illustrating the theory on which the invention is based.

For convenience in describing the invention reference is made to the preferred embodiment thereof illustrated in the accompany drawings and specific language is employed. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, but that various alterations and modifications of the structure, such as could be effected by one skilled in the art, are contemplated.

Referring first to Figures 1 and 2, it will be observed that only the forward (or upper) end of the projectile containing the timing mechanism is disclosed; the body of the projectile containing the main charge may assume any conventional form. Thus the outer wall IE) of the projectile body may be threaded onto a depending annular flange H on the base I2 of the projectile head. A base charge l3 of explosive, for example black powder, is sealed within the lower end of the base I? and is fired by means of a pellet l5 of nitrocellulose or the like which is seated in a passage I'o' communicating with the base charge. The pellet is in turn detonated by a primer ll which may contain fulminate of mercury and black powder. Any suitable form of flashway may be provided between the pellet and the base charge, and the details thus far described constitute no essential feature of novelty of the instant invention but may be modified to a considerable extent.

The base i2 is provided with an upstanding spindle l8 which is threaded to receive the projectile nose It and a nut 20, the latter serving to retain the elements of the timing mechanism in position on the spindle. These elements preferably include a member 2| keyed to the spindle I8 and having a generally disk-shaped base portion 22 and a timing or control member 25, the latter being interposed between the lower face of the member 2i and the upper face of the base 12, which faces are each provided with oppositely directed radial grooves, the grooves 27 in the base member l2 being disposed at right angles to the grooves 26 in the member 2|.

The inertia members are illustrated as comprising balls 30 and Si which are received in the respective grooves 27 and 26 and which extend into grooves 32 and 33 formed in the lower and upper faces respectively of the control member 25. The grooves 32 and 33 are spirally disposed with respect to the axis of the projectile, preferably approximating closely parabolic spirals, the spirals being of opposite hand. Thus as the balls 39 move radially outward in the grooves 21, the control member 25 is rotated by the action of these balls on the outer wall of the spiral groove 32. At the same time, the balls 3| are constrained to move radially inward in the grooves it by the action thereon of the oppositely di reeted spiral groove 33 in the control member 25. The balls 30 and 3| are of slightly different mass, the balls 30 being preferably the heavier, and the difference in the mass of these balls determines the resultant force which is applied to the rota tion of the control member 2'5 as hereinafter more particularly set'forth. The control member is preferably provided in its inner circumference with an annular groove 34 in which are engaged a plurality of anti-friction balls 35 or the like, these balls being disposed at spaced points about the circumference of the spindle l8 and being received in spaced recesses formed in the latter, the balls 35 being retained in position against displacement axially of the spindle lit by a bushing 3?. The balls 35 serve to maintain the control member 25 against axial displacement and out of contact with the adjacent faces of the member 2| and the base 2 to minimize friction.

The nose of the projectile is completed by a fixed annulus 39 and a rotatable annulus 20 which may be provided with suitable cooperating indicia, rotation of the annulus e8 serving to determine the timing. The annulus 59 is frictionally retained in position against accidental displacement by screwing down the nose l9 to apply pressure thereto. A pin 33 and recesses ll in the periphery of the base l2 facilitate rotation of the annulus 30 by suitable tools.

The annulus 49 is provided on its inner face with 2. lug 52 which is positioned for cooperation with a lug 43 secured to or formed integrally with a band do, the latter being received within an annular recess i5 formed in the periphery of the control member 25, the ends of the band being pinned or otherwise secured together as indicated at ill so that the band is frictionally gripped on the periphery of the control member. It will be observed that as the annulus is rotated in a counterclockwise direction as seen in Figure 4, the lug l2 thereon will engage the lug $3 on the band'to rotate the latter. The band is further provided with a spring tongue 33 having a tooth til on the free end thereof functioning as a pawl for engagement with ratchet teeth 59 formed in the control member, so as to prevent clockwise rotation of the band from any position to which it has been set by the annulus 48.

The band M is generally L-shaped in crosssection, the lower flange 52 thereof being nearly continuous but being interrupted as indicated at 53. One end of the flange 52 is provided with a downwardly turned tongue 54 which serves to actuate a detent to release the firing pin. Thus the base E2 is provided with a diametrically disposed aperture 53 which communicates at one end with a recess 59 formed in the periphery of the base, this recess receiving a plate 60 having the inner face thereof grooved as indicated at ti. Received within the aperture 58 is a firing pin detent 63, the latter having secured to one end thereof a lever arm 6 5 which lies within the groove El and which, prior to actuation of the firing mechanism, assumes an inclined position generally defined by the inclined wall 66 of the groove (it. The upper end of the lever arm 6 3 is initially positioned immediately beneath the underside of the flange 52 on the band i l, but is arranged to be engaged by the downwardly extending tongue 54 of this flange as the band and the control member 25 are rotated, so as to force the lever upwardly and thereby rotate the detent 63, Figure 9 illustrating the position of the tongue and lever at the instant of engagement thereof and prior to rotation of the detent.

Detent 63 is journalled for rotation in aperture 53 by means of bushings 68, and is provided adjacent the projectile axis with a laterally bent portion 69 which, when the lever arm 66 is disposed beneath the flange 52 of the band as, is arranged to engage a recess II in the firing pin12 to retain the latter against displacement. The firing pin is received in a radial aperture 13 in the base l2, and is moved outwardly therein by the action of centrifugal force when released by rotation of the detent 63, and when thus moved outwardly strikes and detonates the primer H with the result hereinbefore indicated. Preferably the arrangement is such that while the detent is retaining the firing pin against displacement, the deformed portion 69 of the detent is directed axially of and away from the firing pin aperture 13, so that the tendency of the firing pin to move outwardly is resisted solely by the detent, no force being transmitted to the detent tending to rotate the latter. However, when the detent is given its initial rotational movement, the deformed portion 69 thereof functions as a crank which is thrown off dead center, and thereafter the inertia of the firing pin will itself rotate the detent to the further extent necessary to release the firing pin.

As shown more particularly in Figure 10, stops are provided on the member 2| for cooperation with the lug 43 on the rotatable annulus 4i]. One of these stops, indicated at 82, may consist of a lug which is secured in a recess in the lower face of the member 2|, this lug projecting radially into the path of movement of the lug 43, so as to limit reverse rotation of the latter and of the annulus 50. The second stop, indicated at 83, is preferably in the form of a spring pressed pawl which is displaceable in the direction in which the annulus 4i] and lug 43 are rotated for the purpose of setting the band 44, but which will prevent reverse rotation of the annulus. Initially the parts are assembled with the lug t3 intermediate the stops 82 and 83. As the annulus ie is rotated to set the band 4 3 to determine the timing, the lug 43 moves past the stop 83, and having passed this stop is prevented from returning. By means of this arrangement it is possible to ascertain by an inspection of the cooperating indicia on the annuli 49 and 38 whether the timing device has been displaced out of its initial position. In the absence of such an arrangement, the timing device might be first set to explode the charge after the expiration of a greater period of time than that which is desired, since subsequent rotation of the annulus E0 to set the timing device for a less period would of course not retract the band 44 to a position corresponding to such less period.

The control member 25 may be initially locked against rotation by means of one or more centrifugal detents 75, each of which is received in a recess it in the base I2 and is provided with an upwardly directed tongue Tl arranged to engage with a recess E8 in the periphery of the control member 25. A spring 15, seated in the-detent l5 and bearing against the adjacent inner surface of the annulus 39 normally urges the detent inwardly so that the control member is locked against rotation. Two such detents are preferably provided at diametrically opposite sides of the control member.

It will be observed that these detents perform the further function of resisting axial displacement of the control member 25 at the instant of expulsion of the projectile from the gun. Thus as shown more particularly in Figure 3, the upper ends of the tongues ll of the detents are engaged with the control member 25 and thus the end thrust on the control member as the projectile acquires its maximum velocity in the direction of flight is transmitted directly to the base l2 through the detents l5, thus preventing damage to the more delicate means, including the anti friction balls 35, by which the control member is journalled for rotation.

The mode of operation of the device as thus far described will be apparent. The timing is initially determined by rotation of the annulus 40 which rotates and positions the band 44 on the control member 25, the control member being held against rotation during this operation by the detents 15. When the projectile is fired, the detents 15 are moved radially to release the control member. At the same instant centrifugal force is applied to the balls 30 and 3|, and the balls 30, being heavier than the balls 3|, are moved radially outward, the force thereby applied to the rotation of the control member 25 being resisted by the balls 3| which are forced inwardly. When the control member has been rotated through an angle sufficient, as determined by the initial setting of the band 44, to bring the tongue 54 beneath the lever arm 64, the detent 63 is actuated to release the firing pin and the charge is fired as hereinbefore explained.

As already pointed out, it is an important feature of the invention that the force which tends to rotate the disk, referred to for convenience as the moment, is exerted by each ball independently of the distance of the ball from the axis of rotation of the projectile. In other words, this moment is a constant for all positions of the ball. When this condition is established, it is obvious that if two balls of slightly different mass apply oppositely directed moments to the disk, the resultant moment will be proportional to the difference of the mass of the balls and will be independent of the speed of rotation of the pro- J'ectile on its axis.

It can be shown that the desired result may be achieved by constructing the groove with which each ball engages so that the center of the ball will follow a parabolic spiral having the conventional formula =cR where c is a constant, 0 is the angular displacement, and R is the radius for any given angle 0.

For example, the centrifugal force F of the ball may be represented as follows:

where W is weight in lbs. of the ball;

R is radius in feet;

N is the speed of rotation of the projectile in R. P. M.;

v is linear velocity of the center of the ball in feet per second.

Referring now to Figure 11, which illustrates diagrammatically the position which may be assumed by a ball at either of two radii R1 and R2, and in which are shown the radial groove and portions of the spiral groove in which the ball rides, it is apparent that the moment exerted by the ball tending to rotate the disk is a function of the centrifugal force acting on the ball, the lever arm through which the ball acts and the angular relationship of the curved and radial grooves. In other words, if the line 11 in Figure 11 is normal to a tangent to the outer wall of the curved groove at the point of contact of the ball therewith, x1 is parallel to such tangent, and a1 is the angle between yr and a radius passing through the center of the ball, we can express .00034 WR N .00034 WRQN x cosine a cosine a; 2

lax, R X

cosine ni cosine 01 Since cosine we have the following R1X| RgX2 A 1 2 R R2 Referring now to Figure 12, in which is shown a curve of which the angle 4/ is formed between a tangent to the curve and the radius R to the point of tangency and in which I/ is complementary to the angle a of the preceding Figure 11, it can be shown that so that in terms of polar coordinates the angle a may be defined by the following:

Since we have seen that R tan a=c=constant, we may substitute to derive the following:

cR dR d0 T d0=cRdR integrating In order that the ball may follow a path such that its center traces out a parabolic spiral, the desired spiral may be first laid out by the use of the formula. The curve defining the outer wall of the groove will then be spaced from this spiral by a fixed distance equal approximately to the radius of the ball; this fixed distance is of course measured, at any given point, along the line 1/ (Figure 11) which is normal to the spiral path of the ball center. Actually, this fixed distance will be somewhat less than the radius of the ball since the ball does not engage the outer wall of the groove on that diameter of the ball which is perpendicular to the axis of the spiral. The inner wall of the groove will of course be so constructed as to permit free movement of the ball in the groove without excessive play.

It will be appreciated that in its broader aspect the invention contemplates the provision of means for actuating a firing mechanism, either by release or by initial or prolonged operation of the latter, such means being operable by centrifugal force and functioning substantially independently of rotational speed. By the employment of opposing inertia members, a very fine regulation of the force applied to the control member may be obtained by selection of inertia members having small difference in mass.

It will also be observed that the grooves on the control member and base function as guides and might be reversed in position, the radial grooves being provided on the control member and the spiral grooves on the base. Again, grooves or other guide means may be associated with the inertia member rather than with the control member and base. While the cooperating radial and parabolic spiral grooves are preferred for simplicity and accuracy, modification of the shape of either or both of these grooves Without sacrifice of any of the essential features of the invention may be effected if desired. For example, by proper selection of the cam surfaces it is possible to employ balls of the same mass, the opposing forces being unbalanced by the difference in slope of the two curves.

Frequently a projectile rotates during flight on an axis other than that passing through its structural center; it will be observed that by the provision of a plurality of inertia members spaced at diametrical or equidistant points about the axis of the projectile, compensation for rotation of the projectile about some laterally displaced axis is secured.

While the invention is particularly applicable to explosive projectiles for artillery, it will be noted that many features of the invention are useful in connection with other devices of a similar nature requiring accurate timing. Among these may be mentioned other classes of projectiles, such as torpedoes, flares, and the like.

Having thus described the invention, What is claimed as new and desired to be secured by Letters Patent is:

1. In a timing device for explosive projectiles, the combination with a firing mechanism for the projectile, a support, said support comprising two spaced elements having opposed faces supported in spaced relationship to each other by a spindle element, said support having radial restraining means on said opposed faces, a disc member rotatably mounted on the spindle between said opposed faces, said disc member being provided on opposite faces with oppositely directed parabolic spiral grooves having the pro- J'ectile axis as a center, inertia elements of diferent mass positioned in and freely movable in the grooves and engaging said radial restraining means to thereby restrain motion of the inertia elements in a radial direction only.

2. In a timing device for explosive p jectiles, the combination with a firing mechanism for the projectile, a support, said support comprising two spaced elements having opposed faces supported in spaced relationship to each other, said support having radial restraining means on said opposed faces, a disc member rotatably mounted between said opposed faces, said disc member having opposite faces provided with oppositely directed parabolic spiral guide means having the projectile axis as a center, inertia elements of different mass engaging and freely movable along said guide means and engaging said radial restraining means to thereby restrain motion of the inertia elements in a radial direction only.

NORMAN M. LAKE. 

